Dynamics of Orographic Rain Associated with the Passage of Hurricane Ivan (2004) Over the Appalachian Mountains

The goal of this research is to use the Advanced Research WRF (ARW) model to simulate Hurricane Ivan (2004) in order to improve quantitative precipitation forecast (QPF) and understanding of the dynamics of orographic rainfall associated with the passage of tropical cyclones over the Appalachian Mountains. The simulation results compared well with the observation in terms of track and rainfall distribution, although the precipitation amount is overpredicted by the ARW model. Also, from the ARW simulations we identified several common ingredients responsible for heavy orographic rainfall produced by Hurricane Ivan. Heavy orographic rainfall production appeared to be dominated by the convective available potential energy (CAPE), low-level jet lifting, high precipitation efficiency, and a very moist airstream impinging on the mountains. In addition, we used a simple moisture flux model to estimate the rainfall over the Appalachian Mountains, which showed most of the rainfall was produced by the orography. In this study we are also interested in improving the hurricane track prediction. This is due to the fact that the orographic rain distribution is highly associated with the tropical cyclone (TC) track. In order to improve QPF of the orographically induced rainfall associated with the passage of Hurricane Ivan, we performed sensitivity experiments in the ARW model by using different planetary boundary layer (PBL) schemes and microphysical parameterizations, and deactivating the cumulus parameterization in the inner domain(s). Effects of orography on rainfall will also be studied by removing the Appalachian Mountains terrain.